1. Field of the Invention
This invention relates to a method and apparatus for electrically testing multi-core cables, and more particularly it relates to the defective contact test or withstand-voltage test of the cores of a multi-core cable, such as a communication cable, having a number of cores, each comprising a conductor and a cover for insulating the same, by automatically separating said cores one by one.
2. Description of the Prior Art
Usually, a communication cable is constructed using as a structural unit a pair in which two cores are twisted together or a quad in which four cores are twisted together. Some local communication cables containing a number of cable circuits comprise as many as 2,400 to 3,200 pairs, i.e., 4,800 to 6,400 cores may be contained in a single cable. In the production of such communication cables, the cores have to be tested for defective contact for dielectric breakdown which would take place upon application of a specified voltage, in the intermediate or final stage of cable production in order to guarantee the quality of each cable.
Further, in order to carry out such tests, all the cores have to be stripped of their insulating covers at the both ends of the cable.
However, it would require an enormous amount of time or labor to test the cores by successively selecting and separating a single core from the large group of cores as described above. Therefore, various attempts to mechanically or automatically carry out such electric test of multi-core cables have heretofore been suggested and realized.
For example, there has been developed an apparatus comprising a measuring multi-pole connector or multi-pole insulated terminal stand, to the terminals, of which the cores of a cable are once connected, whereupon the cores are successively and automatically subjected to an insulation test or withstand-voltage test by a measuring instrument through said connector or terminal stand. However, carrying out tests by using such apparatuses takes much time for preparation, connection and disconnection upon completion of the test, and fails to provide an efficient automatic test desired. That is, the preparatory operation for removing the insulating covers from the cores or untwisting the cores twisted in pairs or quads and straightening them in order to connect the cores to the terminals on said connector or terminal stand, the operation for picking up the cores one by one for connection to the terminals or the after-operation for disconnecting the tested cores without damaging them cannot be performed without resort to hands. As a result, these operations require a long time and the ratio which the net time required for inspection and measurement bears to the whole time is small. Thus, even if the measuring operation is automated, it would be impossible to improve the efficiency of operation drastically, since the picking up and connecting operations which occupy the greater part of the process are not automatic.
Further, making a defective contact test or a withstand-voltage test requires application of a relatively high voltage which makes it necessary to provide a substantial distance between adjacent terminals, thus resulting in a disadvantage that the insulated terminal stand or multi-pole connector itself has to be enlarged, and requiring a large operating space.